The present invention relates, in general, to bleaching detergent compositions containing as a bleaching agent a peroxyacid compound, and the application of such compositions to laundering operations. More particularly, the present invention relates to granular bleaching detergent compositions which provide enhanced bleaching performance concomitant with a significant improvement in the stability of the peroxyacid bleaching species in the wash solution.
Bleaching compositions which release active oxygen in the wash solution are extensively described in the prior art and commonly used in laundering operations. In general, such bleaching compositions contain peroxygen compounds, such as, perborates, percarbonates, perphosphates and the like which promote the bleaching activity by forming hydrogen peroxide in aqueous solution. A major drawback attendant to the use of such peroxygen compounds is that they are not optimally effective at the relatively low washing temperatures employed in most household washing machines in the United States, i.e., temperatures in the range of 80.degree. to 130.degree. F. By way of comparison, European wash temperatures are generally substantially higher extending over a range, typically, from 90.degree. to 200.degree. F. However, even in Europe and those other countries which generally presently employ near boiling washing temperatures, there is a trend towards lower temperature laundering.
In an effort to enhance the bleaching activity of peroxygen bleaches, the prior art has employed materials called activators in combination with the peroxygen compounds. It is generally believed that the interaction of the peroxygen compound and the activator results in the formation of a peroxyacid which is a more active bleaching species than hydrogen peroxide at lower temperatures. Numerous compounds have been proposed in the art as activators for peroxygen bleaches among which are included carboxylic acid anhydrides such as those disclosed in U.S. Pat. Nos. 3,298,775; 3,338,839; and 3,532,634; carboxylic esters such as those disclosed in U.S. Pat. No. 2,995,905; N-acyl compounds such as those described in U.S. Pat. Nos. 3,912,648 and 3,919,102; cyanoamines such as described in U.S. Pat. No. 4,199,466; and acyl sulfoamides such as disclosed in U.S. Pat. No. 3,245,913.
The formation and stability of the peroxyacid bleaching species in bleach systems containing a peroxygen compound and an organic activator has been recognized as a problem in the prior art. U.S. Pat. No. 4,255,452 to Leigh, for example, specifically addresses itself to the problem of avoiding the reaction of peroxyacid with peroxygen compound to form what the patent characterizes as "useless products, viz. the corresponding carboxylic acid, molecular oxygen and water". The patent states that such side-reaction is "doubly deleterious since peracid and percompound . . . are destroyed simultaneously." The patentee thereafter describes certain polyphosphonic acid compounds as chelating agents which are said to inhibit the above-described peroxyacid-consuming side reaction and provide an improved bleaching effect. In contrast with the use of these chelating agents, the patentee states that other more commonly known chelating agents, such as, ethylene diamine tetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) are substantially ineffective and do not provide improved bleaching effects. Accordingly, a disadvantage of the bleaching compositions of the Leigh patent is that they necessarily preclude the use of conventional sequestrants, many of which are less expensive and more readily available than the disclosed polyphosphonic acid compounds.
The influence of silicates on the decomposition of peroxyacid in the wash and/or bleaching solution has heretofore gone unrecognized in the art. U.S. Pat. Nos. 3,860,391 and 4,292,575 disclose that silicates are conventionally employed as additives to peroxide-containing bleaching solutions for the purpose of stabilizing peroxide compounds therein. However, the patentees note the fact that the use of silicates in such bleaching solutions may create other problems in the bleaching operations, such as, the formation of silicate precipitates which deposit on the bleached goods. Consequently, the patents are directed to processes for bleaching cellulose fiber with silicate-free bleaching solutions in whch peroxide stability is enhanced with compounds other than silicates.
European Patent Publication No. 28,432, published May 13, 1981, describes on page 7 thereof certain polyphosphonate compounds which "have been found to be uniquely effective in stabilizing organic peroxyacids against the generally deleterious effect of water-insoluble silicates, especially those belonging to the zeolite and kaolin classes". The nature of such "deleterious effect" is not specified. A preferred embodiment of the invention is said to be a granular detergent composition comprising the defined polyphosphonate compound in combination with a water-insoluble silicate and an "organic peroxyacid bleach percursor", more commonly known an as organic activator. Thus, the art has heretofore failed to appreciate or suggest the improved bleaching performance which can be achieved with granular bleaching detergent compositions containing a peroxyacid compound when such compositions are characterized by the absence of silicate compounds of the type conventionally used in detergent compositions.